Etching of oxides from semiconductor wafers has traditionally been accomplished through the use of liquid acids and chemicals sprayed onto such wafers but recently the processing of such wafers with the use of etchant gases, such as anhydrous hydrogen fluoride gas, has become known and is successfully used with a high degree of control. The Blackwood U.S. Pat. No. 4,749,440 shows an elementary form of apparatus for accomplishing the gaseous etching of semiconductor wafers, and an improved etching chamber is illustrated in a prior art pending application Ser. No. 020,473, filed Mar. 2, 1987, now abandoned and under common ownership with the present application. This prior art disclosure illustrates a chamber with an apertured diffuser plate providing for ingress of etchant gas to the wafer being etched, and the same plate provided for the discharge of spent gases after having been used for etching the wafer.